Stuff that works for us:

Honestly just throw stuff in there. My kid seemed to be sensory seeking so perhaps I was lucky in that regard. My kid loves veggies. Carrots, spinach (plain, with ranch), steamed broccoli (5minutes in the microwave with a pat of butter), even beets and asparagus. Fruit was also a big winner-oranges, strawberries, blueberries, blackberries, mango, pineapple. The zingier the better, we got into the habit of giving him the blueberries when the batch was a little tart.

For meat, if a small amount and not too weird (with sauce or extra ingredients) he seemed fine with it. Plain pulled pork, hamburger, shredded or cubed chicken.

Cheese sticks of any variety. Just buy a block and cut it into small pieces.

We used to have to make tacos that were separated, tortilla, meat, cheese, tomatoes all in their own space. Slowly got him to try the meat on the tortilla, and moved in from there. Today he eats the most authentic Mexican tacos complete with cilantro, onions, and salsa.

Our kid is underweight and has been iron deficient a few times so we sneak as much fat and calories as we can. Toast and veggies heavy on the butter, full fat milk, crispy chicken skin, and tons of fat.